The anti-neoplastic drug cisplatin is essential for treating a variety of epithelial and brain tumors. However, it is ototoxic, neurotoxic and nephrotoxic, causing permanent deafness and acute kidney failure in patients treated with these drugs. The cellular distribution of cisplatin has been only detected indirectly via pathological observations, by low-resolution positron emission tomography, autoradiography, or biochemically using high-performance liquid chromatography. The long-term goal of this research is to prevent ototoxicity and permanent deafness. We have developed a fluorescently-tagged cisplatin molecule that is bio-active and can be detected within individual cells in the inner ear, kidney and other organs after systemic administration. In addition, we can use this conjugation procedure to identify cytoplasmic cisplatin-binding proteins that may reveal novel intracellular mechanisms of cytotoxicity or protection. The working hypothesis is: Cisplatin trafficks to cochlear hair cells via endolymph, and binds to cytosolic proteins. The specific aims of this project are to: Aim 1: characterize the cochlear distribution of cisplatin in three rodent models, Aim 2: identify the conditions that modulate cellular uptake of cisplatin in vitro, Aim 3: verify that cisplatin enters cochlear hair cells from endolymph in vivo, Aim 4: identify cisplatin-binding proteins and their distribution in the cochlea. By determining which cells take up cisplatin, the mechanisms by which it enters cells and identifying its protein-binding partners, we can begin to develop new strategies to prevent cisplatin-induced ototoxicity. This will allow clinicians to use cisplatin and related drugs more efficaciously while preserving auditory function, especially important in pediatric patients acquiring language and educational skills. Understanding the mechanisms of how cisplatin crosses the blood-labyrinth barrier to enter the cochlea is crucial to prevent cisplatin-induced ototoxicity. The proposed research will enable the development of new strategies to prevent cochlear uptake of cisplatin and its derivates and subsequent ototoxic sequelae, particularly life-long deafness, tinnitus and vestibular deficits.